Sonic (NASDAQ:SONC) shares plummeted in mid-September after the company reported preliminary same-store-sales results which investors were clearly not happy with. 

After dropping nearly 10% after the results were announced the stock did not recover, ending the month approximately 15% below where it began September, according to S&P Capital IQ data. It was a lesson in expectations versus reality.

In the September 14 press release the company said that yearly same-store sales growth reflected an increase of approximately 6.9% at company drive-ins and 7.3% at franchise drive-ins for the year ended August 31, 2015. The company also announced that systemwide same-store sales for its fourth fiscal quarter increased approximately 4.9% -- growing about 4.5% at company-owned locations and approximately 4.9% at franchise drive-ins for the fourth fiscal quarter. 

Those seem like fairly positive results, but the fourth quarter results pulled down the yearly average and were below what the brand delivered in the third quarter. Investors were clearly expecting better as you can see from what happened to Sonic stock after the announcement was made.

  

Source: YCharts.com

Steady as she goes
While the same-store-sales growth proved underwhelming to stockholders, the company's CEO defended the results based on the chain's performance over the entire year. 

"Fiscal 2015 was a great year for our business and brand. Our multiple initiatives focused on product innovation, multi-day part promotions and effective media, all of which drove annual same-store sales growth of 7.3%. This is particularly noteworthy given our strong performance in fiscal 2014," said Cliff Hudson, Sonic Corp. CEO. "We also completed $124 million of share repurchases and initiated a quarterly dividend building shareholder value."

Hudson's saying positive things but it's hard to say he's spinning the results because these numbers are solid and given that they are yearly totals it's hard to see how they surprised investors. The only shock may have been that sales growth did tail off in the fourth quarter to only 4.9% across all stores -- a dip from 6.1% in the third quarter.

Something to watch
Investors were clearly concerned that they company cooled off a bit in the fourth quarter despite its solid results for the full year. What remains to be seen is whether the slight pullback becomes a trend going forward or whether it's just a minor hiccup.

Clearly stockholders want to see the company maintain 6-7% growth in each quarter, which may be a problem as the company's 2016 guidance calls for "2% to 4% same-store-sales growth for the system." Of course, that may just be setting the bar low in order to be able to exceed the goal and get investors excited again.

Daniel Kline has no position in any stocks mentioned. He had a Master Blast at Sonic last weekend and his son got a slush. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.